A crankcase lubricant is an oil used for general lubrication in an internal combustion engine where an oil sump is situated generally below the crankshaft of the engine and to which circulated oil returns. It is well known to include additives in crankcase lubricants for several purposes.
Phosphorus in the form of dihydrocarbyl dithiophosphate metal salts has been used for many years to provide lubricating oil compositions for internal combustion engines with antiwear properties. The metal may be zinc, an alkali or alkaline earth metal, or aluminium, lead, tin, molybdenum, manganese, nickel or copper. Of these, zinc salts of dihydrocarbyl dithiophosphate (ZDDPs) are most commonly used. However, anticipation of stricter controls on the amount of phosphorus in finished crankcase lubricants has led to the need to provide phosphorus free additives to, at least partially, replace ZDDP in such lubricants.
US 2006/0183647 ('647), now U.S. Pat. No. 7,807,611 B2, addresses this need and describes tartaric compounds in low phosphorus lubricants to provide wear reduction and other properties. The tartaric compounds described include condensation products of a tartaric acid and an amine, specifically described compounds including tartrimides. '647 states that the amines may have the formula RR1NH wherein R and R1 each independently represent H, a hydrocarbon-based radical of 1-150 or 8-30 or 1-30 or 8-150 carbon atoms. '647 specifically describes oleyl tartrimide and tridecylpropoxyamine tartrimide. Thus, '647 exemplifies the presence of relatively long chain groups on the N imide atom. The molecular weight of the imides is thereby enhanced; this means that more weight of additive is required to provide a defined number of moles of the imide.